O₂, or molecular oxygen, is a colorless, odorless gas essential for life on Earth. It makes up about 21% of the atmosphere and is produced primarily by plants through the process of photosynthesis. Animals, including humans, rely on O₂ for respiration, which is how they convert food into energy. Oxygen exists as diatomic molecules, meaning two oxygen atoms bond together to form O₂. This gas is crucial for combustion, supporting fires and various industrial processes. Additionally, O₂ is used in medical settings to assist patients with breathing difficulties and is vital for many chemical reactions in nature and technology.